The present invention generally relates to the recovery of desirable, useful aromatic, that is, odoriferous principles from source material. More specifically, it relates to recovery of product fractions, such as oleoresins, containing the desired aromatic principle from source material such as plant material in which such aromatic principles occur naturally. The term "aromatic" as used herein is intended to refer to the aroma-possessing property of the material; the term is not intended to be confined to the chemical context of possessing an "aromatic" ring structure.
In particular, this invention relates to the recovery of aromatic resin from foliage of coniferous evergreens which contain substantial quantities of maltol (2-methyl-3-hydroxy-4-pyrone). Maltol is a heterocyclic aromatic chemical used extensively in flavor and fragrance compositions. The resin obtained by the process described in the present invention can be used as an ingredient in flavor or fragrance compositions or as a commercial source for the recovery of natural maltol. The invention relates more generally to the improved recovery of maltol and other aromatic principles from other source material, such as resin or other products representing a relatively concentrated form of the desired active relative to its content in native plant material.
The recovery of desirable aromatic principles from plant material generally involves as one step the treatment of all or part of the plant material to recover a resin, oleoresin, or other concentrate, and then treatment of that product to recover the desired aromatic principle in further concentrated or even pure form. The oleoresins recoverable from the coniferous trees are well known in the flavor, fragrance, cosmetic and pharmaceutical industries. The resin extracted from balsam fir (Abias balsamea L.) is the most widely known, and is even allowed to be used in food.
Hundreds of botanical species are used as raw materials and in each case a particular part of the plant such as leaves, stems, bark, fruit or flowers are found to be most suitable. Despite the variety of plant sources and the multitude of solvents that can be used in the extraction process, all known methods have one common basis. This is a preferential solubility and affinity of the aroma determining substances for the chosen solvent. The process of extraction is, in fact, preferable diffusion of aroma carrying chemicals from the plant material into a solvent phase. The chemicals can be concentrated and recovered from the solvent phase by stripping, usually through a distillation process.
Numerous extraction means used for contacting plant material with the solvent are designed to speed up and intensify the diffusion process. Despite the multitude of botanical sources and known extraction techniques, they can be divided into two major groups--those which use dehydrated plant material and those in which the oleoresin is extracted from fresh plant tissues. Cinnamon bark, black pepper, various fruits of the Umbelliferae family such as cumin, caraway, celery, etc. can be used as examples of plant material which is extracted dry. Rose flowers, jasmine, tuberose and lavender are examples of plant material which is extracted fresh.
Hardy raw materials which are mentioned in the first group usually retain their aromatic values through the dehydration process, while gentle tissues of flowers generally completely surrender their aromatic principals. The dehydration process alters the cell structure of the plant tissue, creating pores and cavities accessible to solvents and thus making the diffusion process reasonably quick. The plant material extracted fresh usually consists of flowers with gentle and thin petals which, despite the presence of water, offers low resistance to the diffusion.
The difficulty in conducting the extraction process becomes rather severe when hardy plant material is to be extracted but some or all of the aromatic values do not survive dehydration. Such is the case of a variety of coniferous plants and, in particular, various species of fir. The needles of the fir trees are specifically adapted to a very low rate of water evaporation therefrom and offer hard resistance to the penetration of the solvent. Thus, simple contact of fir needles with solvents results in very slow extraction. Due to the specific shape of the needles, a rough grinding is not efficient either, since breaking of the needle exposes only a small cross section to solvent penetration. It is, of course, possible to grind or to disperse fir needles into very fine particles. Such a process, however, is very expensive and for many reasons impractical.
The presence of maltol in the coniferous trees in general, and in the balsam fir (Abias spp.) specifically, is well established in scientific literature. Maltol has also been reported to be in the bark of some species of larch (Larix spp.) trees. Maltol is present in larch bark in combined form to an extent varying from about 0.1 percent to about 2 percent by weight depending upon the bark layer and the season of harvest. The richest supply of maltol is found in the bark of roots of the larch trees although, for practical reasons, not much root bark is harvested. Large quantities of larch trees and bark containing maltol exist and are available primarily in the northwest part of the United States and southwest Canada,. The bark is available at sawmills where it is stripped off of larch trees and stored in a pile, there to be burned for fuel or otherwise used if economical processes for recovering useful components therefrom can be found.
Limited quantities of fir balsam oleoresin are steadily produced by the extraction of dehydrated fir needles. The yield of oleoresin is rather low and so is the maltol content in it. The product is, therefore, costly and usually is employed only in expensive flavor and fragrance compositions. Due to its high cost and the low content of maltol, fir balsam oleoresin has not been seriously considered to be a practical source for recovery of maltol. Indeed, dehydration of the fir needles causes loss of essential oils, reduction in the yield of oleoresin, and a severe decrease in the maltol content of the product which is thereafter recovered.
Despite the attractiveness of maltol and of oleoresins containing maltol, recovering significant amounts of maltol using known extraction techniques has proven to be difficult or disappointing.
Maltol is insoluble in non-polar hydrocarbons, which renders solvent extraction with such solvents unsuitable for recovering maltol-containing resin from plant material. Although maltol is soluble in hot water, the data in scientific and patent literature indicates that maltol cannot be efficiently recovered from plant material by hot water extraction.
Maltol shows substantial solubility in polar solvents such as acetone, alcohol, and the like. However, these solvents are water soluble and will dissolve not only maltol but also all the eater contained in the fresh plant source material. This property makes subsequent recovery of the oleoresin or the maltol a difficult task. Utilization of water immiscible solvents (in which maltol is still soluble) for the extraction of fresh plant material by conventional techniques is restricted by the presence of water as described above.
In the course of development work aimed at the recovery of maltol from the foliage of coniferous species and, in particular, balsam fir, several drawbacks have been observed.
Oleoresin with high maltol content can only be recovered from fresh fir plant material. Dehydration (whether induced artificially or naturally) of the plant material results in a very substantial decrease of recoverable maltol to the point that the resin extracted from dry needles becomes an unsuitable source for practical recovery of maltol. This creates the necessity to work with fresh needles in the attempt to extract resin with a high maltol content, but leads to further drawbacks.
It has repeatedly been shown that treatment of fresh needles with hot water or steam results in a substantial decrease of recoverable maltol. Although the metabolic cycle of maltol is not clearly known, it may be concluded from scientific literature that maltol undergoes rapid changes in the plant tissue which may be effected by the conditions under which the recovery process is conducted.
The handling of large quantities of fresh plant material presents a serious problem because of the tendency of the plant material to heat up and ferment quickly in a densely pressed form.
In addition, the present inventors have found that woody branches of firs contain practically no maltol and represent undesirable ballast in the extraction process. The presence of thick woody parts soaked with solvent makes the environmentally required cleaning of spent material much more difficult. On the contrary, pure needles can be stripped of the solvent in approximately one-third of the time it takes to clean the mixture of needles and woody parts. However, stripping needles from the branches by physical or mechanical means prior to extracting a maltol-bearing product from the needles is an unacceptably time consuming step.
Thus, there still remains a need for a method for recovering a product fraction comprising a desired aromatic principle, and particularly maltol-containing oleoresin, from a source such as plant material.
It is an object of the present invention to improve the recovery of oleoresins from source material including fresh plant material.
It is another object of the present invention to reduce or eliminate the deleterious effect of plant material dehydration on the maltol content. It is thus a further object of the present invention to increase the recoverable maltol content of plant material.
Another object of the Present invention is to enable aromatic principles such as maltol to be recovered from source material more readily using materials (including solvents) which pose a lessened risk, or no risk, of hazard to personnel handling them and to the environment.
Yet another object of the present invention is to facilitate the separation of fresh needles from the woody branches of coniferous species.
A further object of the present invention is to reduce or eliminate the tendency of stored fresh plant material to undergo spontaneous heating and/or fermentation and/or composting when such a tendency is not desired.